My invention pertains to a vital, lowest speed command selector for train control systems. More particularly, the invention discloses an apparatus arrangement to assure the selection of the lowest active speed command to control a train in the event that more than one allowed speed is registered by the train carried apparatus in a train speed control system.
A speed control system for a train normally includes a wayside arrangement to transmit a selected speed command through the rails, each different command having a distinct code pattern or frequency depending upon the type of system involved. The system further includes apparatus on each train to receive the speed command, such apparatus including frequency sensitive code filters or decoders to determine and interpret which command has been received. Finally, speed governor apparatus is provided, having a separate input from each speed command decoder, which processes and compares the received speed command with a signal indicating the actual train speed to determine if an overspeed condition exists. This governor will hold the train brakes released only when the actual speed is determined to be less than the allowable speed command. These code filters or decoders are designed so that they should never produce an output signal in the absence of the corresponding frequency or code input from the rails. However, to meet added assurance and safety measures which may be required by some installation specifications, it is desirable to be able to assure that, if two code filter, decoder outputs should inadvertently occur simultaneously, the speed governor will receive and respond only to the lower speed command of the two outputs. Therefore, it is advantageous to have a simple circuit arrangement which may be interposed between the bank of filter decoders and the speed governor to assure that the lowest speed filter decoder operating makes all higher speed decoders inoperable.
Accordingly, an object of my invention is a vital lowest speed command selector for a train speed control system.
Another object of the invention is apparatus which assures that only the lowest active speed decoder in a train speed control system is effective to control the speed governor.
A further object of my invention is a simple circuit arrangement which may be interposed between the speed command filter-decoders and the speed governor on a train equipped with a speed control system to vitally guarantee that the lowest operating filter decoder inhibits the operation of all higher speed command filter decoders.
Also an object of the invention is a train speed control arrangement which provides a relay connected to the output of each speed command filter decoder, which relay when energized completes the circuit for applying the speed command output to the train speed governor and further interrupts the supply of operating energy to all filter decoders associated with higher speed commands, to assure that only the lowest detected speed command is effective to control the speed governor and thus the operation of the train.
Other objects, features, and advantages of my invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawing.